The present application relates to eyeglasses, and more particularly to the fitting and installing of a lens in an eyeglass frame.
Many eyeglass frames are a wire rim type which may be either an all metal rim or a metal-plastic combination where the plastic material supplements the wire rims about the lens, usually as a bridge and brow portion. Other eyeglass frames are entirely made of plastic. In each instance, the rim, either of metal or plastic, which holds the lens is commonly called an eye wire. If the eye wire is of metal, it is necessarily separated at a suitable point, usually near the temple hinge of the frame, so that the eye wire may be opened, and in this manner expanded, to receive the lens. A screw connection, at the separation, can pull the ends of the eye wire together after a lens is fitted in place. If the eye wire is of plastic, it is necessarily stretched, or expanded, as by heat, to receive the lens.
Eyeglasses are manufactured in a number of styles with lenses of various shapes, including circular, oval and somewhat rectangular forms. In each instance, the eyeglass frame and especially the eye wires, must be shaped to match the lens. However, the lenses are ordinarily secured from the factory as circular members and each optician has facilities to grind and shape the edges of the lens to fit in a frame selected by the patient, with the final fitting of the lenses in the frame being done by the optician.
It is essential that a lens fit tightly in an eye wire frame or the lens is apt to fall out of the rim and be lost or broken. To facilitate such a fit, an eye wire rim is formed with an internal, V-shaped channel to receive a V-shaped edge of the lens, so cut when the lens is ground. The fit of a lens in a plastic frame is usually tight where the plastic eye wire of the frame is heated and expanded to receive the lens and thereafter cooled to shrink upon the lens. When fitting a frame with a metal eye wire, the lens is positioned in the rim, the screw takes up the separated ends of the eye wire, normally to provide the desirable tight fit. When the fit is tight, the lens may be used for a long period of time without becoming loose.
The edge of a lens is normally ground according to a template available for the purpose, which will match the style of frame being used, and desirably, a substantially perfect fit will be attained. However, as a practical matter, this desirable, perfect fit does not always occur, and in many instances, the lens will be slightly larger or slightly smaller than the inner periphery of the eye wire. If the lens is larger, it is a simple matter to grind its edges until a fit is obtained. If, on the other hand, the lens is smaller than the inner periphery of a metal eye wire, the fit will be loose, even though the screw is fully taken up. When this occurs, and it does so frequently, it becomes necessary to fill a portion of the eye wire channel to securely hold the lens in place. The same problem can occur in a frame having a plastic eye wire, especially where the plastic is nylon which does not easily expand or shrink.
A common material for filling the metal eye wire channel to facilitate fitting an undersize lens in an eye wire frame consists of thin, plastic strips which may be channel shaped to fit better in the eye wire channel and also to provide a seat for receiving the V-shaped edge of the lens. An optician normally cuts a selected length of this filler strip which, in his judgment, will compensate for the looseness of the lens in the frame. He will then place this strip in position and, if his guess is correct, he can then tighten the tube screw to hold the lens in place. These strips do not solve the problem completely for a number of reasons. In the first place, it is a matter of guessing or cut-and-try to select a proper length of a strip in order to obtain a suitable fit. The problems with these filler strips may not end when the optician uses them to fit a lens in place in a frame. Filler strips are also necessary for a thick lens with a sharp edge such as the type used after cataract operations. A thick lens with a sharp edge cannot be effectively seated within and against a metal rim without the risk of chipping an edge of the lens. Accordingly, a filler strip forming a resilient seat is desirable for such sharp-edged lenses.
Sometimes, over a period of use, perhaps as much as a year or two, vibration or movements imparted to the frame of the glasses will cause such strips to slip out of place and become lost and thereafter, the lens will become loose in the eye wire rim to eventually fall out of the rim. Another difficulty with such strips is due to the fact that such filler strips are unsuited to compensate for small spaces or gaps where the contour of the edge of the glasses is not similar to the contour of the eye wire rim. Thus, for a tight fit, several short lengths of filler strip must be placed on each other to fill the gap. In this situation, there is a good probability that the filler strips will soon slip out of place and be lost.